1. Field of the Invention
This invention relates to television signal processing apparatus.
2. Description of the Prior Art
When a moving picture is sampled, as with a television scanning system, the requirement for synchronization is introduced because each part of the signal thus produced must be uniquely identified in time and space. In analog television signals, line, field and frame synchronizing signals achieve this identification. However, the time constraints on these synchronizing signals relative to each point in the picture are very severe in order to achieve the necessary unique identification. In processing the analog television signal, this high degree of accuracy and stability must be maintained.
If the television signal is sampled again, as in a digital video processing system, the constraints change. Thus a sampling frequency is selected such that a precise number of samples are derived from each video scanning line, and the samples have a precise phase relative to each other. At the time of sampling the time constraints are higher than those for the analog system, but after sampling the time constraints may be relaxed because every sample can be uniquely identified merely by calculating its position relative to a digital line synchronizing signal and a digital frame synchronizing signal in terms of samples.
However, a problem arises in that the digital television signal has at some stage to be re-converted to an analog television signal and for that reason it has normally been the practice to maintain the analog timing constraints throughout the digital processing.